IBO2010 Practical 2

IBO 2010 KOREA

PRACTICAL TEST 2

PHYSIOLOGY AND ANATOMY

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Student Code: ___________

Country Code: ___________

The 21st INTERNATIONAL BIOLOGY OLYMPIAD

11th

– 18th

July, 2010

Changwon, KOREA

PRACTICAL TEST 2


Total Points: 49

Duration: 90 minutes

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Dear Participants,

In this test, you have been given the following 2 tasks:

Task I: The response of the rat cerebral cortex to skin stimulation (25 points)

Task II: Anatomy of spider (24 points)

Write down your results and answers in the Answer Sheet. Answers written in the Question

Paper will not be evaluated.

Please make sure that you have received all the materials listed for each task. If any of the listed

items is missing, please raise your hand.

If you have any problem with your computer, raise your hand.

Stop answering and put down your pencil immediately after the end bell rings. The supervisor will

collect the Question Paper and the Answer Sheet.

Note: All animals used in the pictures and the described experiments were treated according

to guidelines approved by the institutional animal care and use committee and

conformed to the NIH guidelines on care and use of animals in research.

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This practical test is composed of 2 tasks.

TASK I. (25 points) The response of the rat cerebral cortex to skin stimulation

Welcome to the Electro-Physiology Laboratory!

Today you are going to examine one of the principles of how the brain works. This test is

composed of 4 parts: one background section on how electrophysiological experiments are

conducted and three experimental sections. You are required to answer a total of 15 questions by

analyzing data presented on screen.

The home-page photo of the notebook computer shows the tools and equipment used in an

electrophysiology laboratory.

Press above the photo

The primary somatosensory (S1) cortex receives tactile information from a specific body

surface region. These specialized receptive areas in the human brain is shown in Figure 1. A

similar body representation within the rat S1 (Fig. 2) will be created from these experiments.

Press

or

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1. Background information

1.1 Skull immobilization with brain exposure

The stereotaxic device is used to immobilize the skull (Fig. 3). The incisor bar is adjusted to

make the skull surface horizontal (Fig. 4). Following a scalp incision, a hole is drilled in the skull

over the location of S1, and a recording electrode (a red, moving needle) is inserted into the brain

(Fig. 5). A micro-driver is used to move the electrode downward (25 μm/step) from the surface

into the brain (Fig. 6).

Press

or

1.2 S1 neuronal response following skin stimulation

The rat skin can be stimulated either mechanically with a cotton probe or electrically with an

electrode. Following the electrical stimulation of forepaw digit (Fig. 7; a white, moving arrow),

S1 neuronal activity is recorded using an electrode (Fig. 7; a red, moving needle). Using an

oscilloscope (Fig. 8), S1 neuronal activity can be visualized (Fig. 9).

Press

or

1.3 Response histogram

When an S1 neuron is responsive to the stimulation of a body part, the body part is within the

receptive field (RF) of the neuron; a neuron does not show any response to the stimulation of

body parts outside of its specified RF.

Using the amplifier (Fig. 10) and the analyzer (Fig. 11), activities of many S1 neurons

surrounding the electrode can be recorded (Fig. 12; left panel). Subsequently, single neuronal

activities can be isolated (Fig. 12; spikes on the right panel). To quantify the S1 neuronal

responses, the stimulation of the body part is repeated within a certain period of time, and the

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action potentials are accumulated to produce a histogram (Fig. 13). In the histogram, the X-axis

stands for time (ms) before (-), the exact moment of (0), and after (+) stimulation. The Y-axis

represents the mean firing rate (Hz) within the recorded neuron.

Press

or

2. S1 neuronal response to forepaw digit stimulation

2.1. Forepaw digit region in S1

For the location of recording electrode, x-y coordinates are drawn over the skull (Fig. 14). The

point where three bones meet (the bregma) is the origin (0, 0) of the coordinate system. Previous

investigations reported that the point (0.3, 4.3) (Fig. 15) is one of the responding spots for

stimulation of the 2nd forepaw digit (Fig. 16).

Press

or

2.2. Mechanical stimulation

To find the general boundaries of the S1 region responding to stimulation of a specific skin

area, it is better to perform mechanical stimulation prior to electrical stimulation. A recording

electrode is positioned above the coordinate (0.3, 4.3) and is lowered stepwise at 25 μm/step

(Fig. 17; a red, moving needle). The responses to mechanical stimulation of the 2nd forepaw digit

are given in Table 2.2

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Table 2.2

Fig. Depth

(number of steps)

Area of

skin stimulation

S1 response to

skin stimulation

S1 Response to

joint movement

18 0-30 Broad Weak no

19 31-48 Tip Strong no

20 49-60 Broad Weak strong

Press

or

2.3 Electrical stimulation

A stimulating electrode is inserted into the 2nd forepaw digit, whereas the recording electrode is

inserted into the S1. The measured distance from the stimulating electrode to the recording one is

12 cm. The response of the S1 neuron to weak and strong stimuli is shown in Table 2.3. and

Figures 21 and 22. (Note the pop-up histogram at the bottom in both actions.).

Table 2.3

Action Stimulus to 2nd forepaw digit Response of S1 neuron

Cursor on 21 Weak (0.1 mA) No conspicuous spike

Cursor on 22 Strong (2 mA) One conspicuous spike

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Q1. (1 point) Based on the results of mechanical and electrical stimulation, which of the

following statements is correct?

A. The strongest response to mechanical stimulation is observed in neurons at 0.5-

0.75 mm deep from the surface.

B. Neurons at a depth of 0.775-1.2 mm respond to the smallest skin area.

C. Neurons at a depth of 0.775-1.5 mm respond only to skin touch.

D. The thickness of the S1 cortex is less than 1mm.

E. The firing rate (Hz) of S1 neurons has no correlation with stimulus intensity.

Q2. (1 point) Calculate the minimum (p) and maximum (q) velocities (unit: m/sec) of

information transmission from the digit to the S1.

Q3. (1 point) During the period of 6-15 ms after stimulation, what is the net increase in the mean

value ( ) of firing rate (Hz) evoked by strong (2 mA) stimulation?

2.4. Response to a gamma-aminobutyric acid (GABA) antagonist

GABA is a neurotransmitter in the brain. The response of the S1 neuron to weak and strong

stimuli following the topical application of a GABA antagonist (i.e., inhibitor of GABA action)

to the S1 cortex is shown in Table 2.4 and Figures 23 and 24. (Note the pop-up histogram at the

bottom in both cases.).

Table 2.4

Action Stimulus to 2nd forepaw Response of S1 neuron

Cursor on 23 Weak (0.1 mA) No conspicuous spike

Cursor on 24 Strong (2 mA) Two conspicuous spikes

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Q4. (2 points) Based on the results of before and after the antagonist application, which of the

following statements is correct?

A. The net increase in the mean firing rate (Hz) of the first peak in histogram 24 is about

2.14 times of that of the peak in histogram 22.

B. After the antagonist application, the mean firing rates (Hz) always increase regardless of

stimulation intensity.

C. The GABA antagonist inhibits excitatory synaptic activity in the S1.

D. Based on histogram 24, a net increase in the mean firing rate (Hz) for the first peak is 4.5

times of the one for the second peak.

E. The second peak in histogram 24 is not associated with S1 processing of the cutaneous

input from the digit.

Press

or

3. S1 neuronal response to hindpaw digit stimulation

3.1 Electrical stimulation

Previous investigations reported that the point (-1.0, 2.5) is one of the responding spots for

hindpaw digit stimulation (Fig. 25).

A recording electrode is lowered stepwise (25 μm/step) downward from the brain surface.

Responses of neurons at three locations (a=25 steps, b=41 steps, c=52 steps) along the vertical

track are recorded (Fig. 26).

Following strong (2mA) electrical stimulation of the 2nd, 3rd, and 4th hindpaw digits (Fig. 27),

responses of the three neurons at a, b, and c are recorded (Fig. 29).

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3.2 Response to local anesthesia

A local anesthetic drug applied to the 3rd hindpaw digit (Fig. 28, grey color) causes a sensory

loss within 2 minutes, and the effect lasts for 30 minutes. Afterward, recovery of sensation

gradually occurs. The drug effect completely disappears by 60 minutes post-application. When

strong (2 mA) electrical stimulation is applied to the digit 40 minutes after drug application, the

response of the three neurons is changed (Fig. 30).

Q5. (1 point) Based on neural response before anesthesia (Fig. 29), choose the correct statement.

Case Neurons Stronger or longer response Weaker or shorter response

A Locations a, b and c 2nd digit 3rd digit

B Locations a, b and c 4th digit 3rd digit

C Location b 4th digit 2nd digit

D During 3rd digit stimulation, neurons at locations a and c have longer response

durations than neuron at location b.

E Location a 4th digit Other digits

Q6. (1 point) Based on neural response before anesthesia (Fig. 29), choose the correct statement.

A. All three neurons respond to 4th digit stimulation.

B. A single S1 neuron responds to the stimulation of only one digit.

C. Neurons at location a respond to the stimulation of more of the hindpaw digits than

neurons at location b.

D. Neurons at location c respond to the stimulation of more of the hindpaw digits than

neurons at location b.

E. All three neurons receive convergent sensory information from two or more digits.

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Q7. (1 point) Based on the responses shown by the neurons in all three locations in Figs. 29 and

30, choose the incorrect statement.

Case Location of stimulation Timing of response Magnitude of response

A 2nd digit 40 min after drug application Increased

B 3rd digit 40 min after drug application Decreased

C 4th digit 40 min after drug application Increased

D 2nd and 4th digits Before and after drug

application

Greater in 4th than in 2nd

digit

E A neuron not responding to a certain stimulus may respond to it under certain

conditions

Q8. (2 points) Based on the response after anesthesia (Fig. 30), select an appropriate inference.

A. The drug is absorbed into the blood and is transferred to the S1.

B. The drug has changed the structure of peripheral nerve branches.

C. Neuronal response is not altered after local anesthesia.

D. The drug causes reversible, temporary changes in S1 neuronal synapses.

E. The change in response after anesthesia is due to newly-synthesized proteins within the

S1.

Press

or

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4. S1 body map

4.1 Normal S1 map

Following repeated stimulation/recording procedures, the normal S1 body map (Fig.

31) is obtained (Note: the electrode is moved along the x or y axis by the distance of 0.5

mm). If the computer cursor is laid on each symbol (○, ●, ▲, □), the abbreviation for

appropriate body surface is shown as a note and, at the same time, the equivalent body

position will be depicted

at the bottom. The

following table provides

the anatomical term for

each abbreviation used

in the figure.

Abbreviations

forelimb

fl forelimb

fp forepaw

fpd 1-5 forepaw digits 1-5

fm forelimb muscle

hindlimb

hl hindlimb

hp hindpaw

hpd 1-5 hindpaw digits 1-5

hm hindlimb muscle

trunk t trunk

vibrissa

mv mystacial vibrissa

rv rostral vibrissa

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Q9. (5 points = 0.5 10) Find the following points (n=10) from Fig. 31 and fill in the

blanks with

abbreviations (i.e., notes within the boxes of the screen) for body surfaces.

Q10. (1point) Based on the answers to Q9, which of the following statements is correct?

A. The fpd4 region is medial to the fpd2 region.

B. The hpd2 region is medial to the hpd4 region.

C. The fl region is rostral to the hp region.

D. The fl region is caudal to the t region.

E. The mvB2 region is lateral to the mvA3 region.

Q11. (1 point) Based on the normal S1 map, what can you conclude about the following areas?

Case Smaller area Larger area

A Forelimb (fl + fp + fpd + fm) Hindlimb (hl + hp + hpd + hm)

B Forelimb (fl + fp + fpd + fm) Trunk (t)

C Hindlimb (hl + hp + hpd + hm) Trunk (t)

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Q12. (1 point = 0.5 2) In the hindlimb region, S1 neurons receiving sensory information overlap

with the motor neurons that cause muscle contraction. Find a coordinate (unit: mm) which

supports this observation.

Press

or

4.2 Change in S1 body map after digit amputation

By reducing the distance between checkpoints (Note: the electrode is moved along the x or y

axis by the distance of 0.2 mm), a more precise map for the hindpaw region is obtained (Fig. 32).

Surgery is performed to remove the 4th hindpaw digit. At 4 weeks after digit amputation, a new

body map is obtained (Fig. 33).

Q13. (4 points = 0.5 8) Put the cursor on the corresponding spots within Figs. 32 and 33, and

notice where the post-amputation response is different from the normal response. For the

locations where alterations occurred, fill in the appropriate table boxes with the

abbreviations (i.e., notes within the boxes of the screen) for the digit numbers (you will fill

in 4 boxes on each table, for a total of 8 boxes).

Normal hpd4 amputated lateral lateral

2.8 2.8

2.6 2.6

2.4 2.4

D Mystacial vibrissa (mv) Rostral vibrissa (rv)

E Forelimb (fl + fp + fpd + fm) Vibrissa (mv + rv)

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2.2 2.2

(mm) 0.6 0.8 1.0 1.2 (mm) 0.6 0.8 1.0 1.2

→ caudal → caudal

Q14. (1 point) What changes occurred in the S1 body map after digit amputation?

Case Activation of neurons by stimulation of Became responsive to

A hpd3 hpd2

B hpd3 hpd2 or hpd5

C hpd4 hpd2

D hpd4 hpd3 or hpd5

E hpd5 hpd2 or hpd3

4.3 Biochemical and histological changes after digit amputation

(1) Biochemical changes (Fig. 34)

Glutamate is a neurotransmitter. To explore the molecular basis of S1-body-map

reorganization following amputation, changes in the amount of glutamate- and GABA- receptors

in S1 tissue were tracked over an extended period of time. The amount of glutamate-receptors

(green curve) increased by 250% of control (dotted line) at 1 week after the 4th hindpaw digit

amputation; whereas, the amount of GABA-receptors (blue curve) rose to 180% of control at 4

weeks post-amputation.

(2) Histological changes (Fig. 35)

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Using transverse sections of S1 tissue, the location of glutamate- or GABA-receptors on the

neuronal surface can be visualized using antibodies against those receptors. Immunostaining of

the S1 cell surface (asterisks) shows that glutamate-receptors (a and c, arrows) increase at 1

week post-amputation, whereas GABA-receptors (b and d, arrows) rise at 4 weeks post-

amputation.

Q15. (2 points) Based on Figs. 33, 34, and 35, choose the incorrect statement.

A. An increase in neuronal excitability is observed at 1 week after amputation.

B. An increase in neuronal inhibition is observed 4 weeks after amputation.

C. In the normal state, the S1 body map is maintained by a balance between excitatory

sensory input and local inhibition within the cortex.

D. During 1-4 weeks after amputation, the balance between excitatory input and local

inhibition is always maintained.

E. Electrophysiological changes at 4 week after amputation are accompanied by biochemical

and histological changes in S1 tissue.

Hope you’ve got interested in Neuroscience.

Press

Let’s dissect a spider and be a Spiderman!

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TASK II. (24 points) Anatomy of spider

Caution: Handle carefully, because only one spider will be provided for each student.

Please note that the vials are labeled Venom gland, Silk gland, Heart, and Book lung in

English.

This task is composed of 2 parts.

Part I. (14 points) Exploration of the spider cephalothorax.

Q16. Both spiders and insects are members of phylum Arthropoda. In general, insects have two

kinds of eyes; compound eye and single eyes (ocelli). Examine the spider specimen

carefully under the microscope and answer the following questions.

Q16.1. (2 points) Record the types and total number of the spider's eyes.

Q16.2. (2 points) Generally, spider’s eyes are arranged around its head in two distinct rows; i.e.

the anterior and posterior rows. Within each row, the inner pair of eyes are designated

as medial, while the outer pair is described as lateral (Table 1). Each eye is defined

using two anatomical terms: anterior vs. posterior and medial vs. lateral. Examine the

specimen and draw the relative position of eyes in the figure on the Answer Sheet.

Label the drawn eyes with specific codes given in Table 2.

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Table 1. Terms of anatomical position

Anterior situated near or toward the head

Posterior opposite of anterior

Medial toward the midline of the body

Lateral away from the midline

Table 2. Codes for spider eyes

Code Terminology of spider eyes

AME Anterior Medial Eye

ALE Anterior Lateral Eye

PME Posterior Medial Eye

PLE Posterior Lateral Eye

Q17. Spiders can be divided into two suborders based on the positions of the cheliceral fangs.

Using the forceps, examine the movement of the spider fangs under the dissecting

microscope. Then, answer the following questions.

Q17.1. (1 point) What is the striking direction of the fangs?

A from forwards to downwards

B from downwards to forwards

C from inside to outside

D from side to center

E from center to side

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Q17.2. (1 point) The fang forms an articulation (or joint) with the chelicerae. What type of

joint is the articulation?

A Plane joint

B Pivot joint

C Hinge joint

D Saddle joint

E Ball-and-socket joint

Q18. (1 point) As arthropods, spiders have segmented bodies with jointed limbs. The head is

composed of several segments that fuse during development. Being chelicerates, their

bodies consist of two segments – the cephalothorax and the abdomen (Figure 1).

Figure 1. Diagram of spider

Which of the following (1~4) correctly represents the segmental differentiation of the

cephalothorax in spiders compared to Trilobite, an ancient chelicerate?

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Eye Eye Eye

Eye

Eye

A

A

A

L

C

P

C

P

L

P

C

P

C

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

Body Body Body Body Body

Trilobite

1

2

3

4

<Abbreviations>

A: Antenna, C: Chelicera, L: Leg, P: Pedipalp

Caution: From now on, you will dissect the internal organs (venom glands, silk gland, heart, and

book lung) of the spider. Using the Ringer’s solution provided, you need to keep the

dissected organs from drying. You will be scored based on the correctness and the

intactness of the preparation. Points will be deducted when there is a failure to remove

the correct organ.

Q19. Most spiders possess venom that is injected into prey through the fangs of the chelicerae.

Spiders have a pair of venom glands that lie either in the chelicerae or in front of the

cephalothorax (see the diagram of spider in Figure 1). The venom gland consists of an

outermost muscle layer, an underlying secretion layer and a duct. Locate the venom glands

of the spider provided.

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Q19.1. (2 points) Dissect out the pair of venom glands from the spider and put it in the vial

labeled Venom gland after the following examination. It is not required to separate the

venom glands from the chelicerae.

Q19.2 (1 point) Examine the outermost muscle layer of the venom gland under the microscope.

What is the direction of the muscular orientation?

A Longitudinal direction

B Circular direction

C Spiral direction

D Bilateral direction

E Irregular direction

Q20. (2 points) In most spiders, each leg has several segments and the tip of the last segment has

claws. Remove the 1st and 2nd legs from the spider body. Using the microscope, count the

number of segments and claws on each leg.

Q21. Many spider species exhibit sexual dimorphism. In sexually mature male spiders, the final

segment of the pedipalp develops into a complicated structure that is used to transfer sperm

to the female during mating. This apparatus makes the male palp so enlarged that it is often

described as resembling a boxing glove.

Q21.1. (1 point) Examine the external morphology of the spider specimen provided and

identify the sex of the spider.

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Q21.2. (1 point) Pedipalps of spiders also have segmentation like the legs. Using the

microscope, count the number of the segments and claws in each pedipalp.

Part II. (10 points) Exploration of the spider abdomen.

Q22. (1 point) The abdomen and cephalothorax of a spider are connected by a thin waist called

the pedicel, which allows the abdomen to move in all directions (see the diagram of spider

in Figure 1).

Which of the following organ systems does not pass through the pedicel?

A Nervous system

B Respiratory system

C Circulatory system

D Digestive system

E Integumentary system

Q23. The silk-spinning apparatus of the spider is located at the posterior end of the ventral

abdomen. This apparatus is composed of three pairs of spinnerets. Generally, the spinnerets

are arranged in two distinct rows; anterior and posterior. Anatomically, the inner pair of

spinnerets is defined as medial, and the outer pair is lateral (Table 3). Accordingly, the

position of a spinneret is defined using these two positional terms.

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Q23.1. (1 point) Compare the external morphology of the spinnerets with the following

diagram. Label each spinneret in the answer sheet using the codes given in Table 3.

Table 3. Spider spinnerets

Code Position of spinneret

A Anterior

AM Anterior medial

AL Anterior lateral

P Posterior

PM Posterior medial

PL Posterior lateral

Q23.2. (1 point) Identify the structure posterior to the spinneret under the microscope .

A Anus

B Spermatheca

C Spiracle

D Copulatory organ

E Spinneret

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Q24. Spiders produce various kinds of silk fibers from the silk glands. There are seven gland

types in the specimen provided, each producing a different type of silk (Table 4).

Table 4. Silk glands of the spider

Code of silk gland Number of pairs Connection to spinneret

A Numerous Middle & posterior

B 2 Posterior

C 1 Posterior

D 1 Anterior

E 1 Middle

F Numerous Anterior

G 3 Middle (1) & posterior (2)

Q24.1. (1 point) Dragline silk is produced by the largest silk glands of this spider (Figure 2).

Use the codes in Table 4 to locate the largest silk gland.

Figure 2. The silk gland which produces dragline silk

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Q24.2. (2 points) Dissect one complete silk gland which produces dragline silk from this

spider. After dissecting the silk gland, place the organ in the vial labeled Silk gland.

Q25. (2 points) With reference to Figure 1, dissect the heart tube from the abdomen and place it

in the vial labeled Heart.

Q26. (2 points) With reference to Figure 1, locate and dissect one complete book lung. Place the

organ in the vial labeled Book lung.

PRACTICAL TEST 2

Answer Key


Total Points: 49

Duration: 90 minutes

1

TASK I. (25 points)

Q1. (1 point)

A B C D E

√

Q2. (1 point = 0.5 x 2)

p 8

q 20

Q3. (1 point)

40 Hz

Q4. (2 points)

A B C D E

√

Q5. (1 point)

A B C D E

√

Q6. (1 point)

A B C D E

√

Q7. (1 point)

A B C D E

2

√

Q8. (2 points)

A B C D E

√

Q9. (5 points = 0.5 x 10)

Q10. (1 point)

A B C D E

√

Q11. (1 point)

A B C D E

√

Q12. (1 point = 0.5 x 2)

x 0

3

y 2.5

4

Q13. (4 points = 0.5 x 8)

Q14. (1 point)

A B C D E

√

Q15. (2 points)

A B C D E

√

TASK II. (24 points)

Part I. (14 points)

Q16.1. (2 points = 1 2)

Type of eye Total number of eye

Compound eye 0

Ocellus 8

5

Q16.2. (2 points)

Frontal view of the head.

1. 1 point will be given if you draw 4 pairs of eyes at proper position.

1 point to the 4 correct codes (1 point = 0.25 4).

2. 1 point will be given if you draw 4 pairs of eyes at proper position without correct codes or

with incorrect codes.

3. 0 point will be given if you draw incorrect number of eyes.

Q17.1. (1 point)

A B C D E

√

Q17.2. (1 point)

A B C D E

√

Q18. (1 point)

① ② ③ ④

6

√

Q19.1. (2 points)

(Place the organ in the provided vial, labeled Venom gland in English)

1. 2 points will be given if you dissect out a pair of venom glands with or without chelicerae.

2. 1 point will be given if you dissect out the chelicerae with one venom gland.

3. 0 point will be given if you dissect incorrect organ.

Q19.2. (1 point)

A B C D E

√

Q20. (2 points = 0.5 4)

1st leg 2nd leg

Number of segments 7 7

Number of claws 3 3

Q21.1. (1 point)

Sex of the spider provided

Male Female

√

Q21.2. (1 point = 0.5 2)

Number of the segments 6

7

Number of claws 1

Part II. (10 points)

Q22. (1 point)

A B C D E

√

Q23.1. (1 point = 0.5 2)

Q23.2. (1 point)

A B C D E

√

A

PL

8

Q24.1. (1 point)

Code of silk

gland D

Q24.2. (2 points)

(Place the organ in the provided vial, labeled Silk gland in English.)

1. 2 points will be given if you dissect proper silk gland with both regions of ampulla and tail.

2. 1 point will be given if you dissect proper silk gland with ampulla region only.

3. 0 point will be given if you dissect incorrect silk gland.

Q25. (2 points)

(Place the organ in the provided vial, labeled Heart in English.)

Q26. (2 points)

(Place the organ in the provided vial, labeled Book lung in English.)

IBO2010 Practical 2

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